I have a Ram mount for my iphone and a Ram Otter box for the iphone and have used both successfully on my spyder, all the way to LA last year and to Missouri this year. The vibration does not seem to bother it a bit. Make sure you don't have the settings at shake to change songs though, or the vibration will make a difference. But since I have the iphone set up to carry, I don't need XM Radio, I just use Pandora, it is free. I also can download a stream from PandoraJam to keep available for when I may be out of signal. I also use a GPS on my phone when I travel and I play the music in the background. It is very nice. I have my BRP back powered so I have the phone plugged in the whole time and don't have to worry about battery life. Just another option.
But not to hijack the thread, if you want XM, the answer to your question is that you should be able to get your dock secure enough that the vibration won't bother it. This is just based on my experience with the RAM mounts and my iphone.